Only conjecture and heresy
Conjecture, which we have explored in previous threads. The only things we have, that are substantive, may be the artifacts which have been reported:
1] They are unissued, perhaps unfired
2] They are a collection of near-Armistice parts, some pickled and not 'stoved', others appearing to be defective/rejected parts.
3] The quality of assemblage is not as consistent, nor to the standard of serial-production examples.
4] The bayonets are all from earlier rifles, or gunshow replacements from a latter-day.
5] None are import marked, so one might think them souvenirs.
6] Some have incorrect sight leafs, and will not shoot to point of aim.
7] They all have 'type 2' factory receivers, some of the later type.
8] The font on the numbered examples is very different from that used upon serialized rifles.
9] The bolt-stems, when marked, are numbered upon the outboard side.
0] They have a 'sticky' bolt-cap, which requires detenting the striker, and the use of a gripping tool, for removal.
1] Headspace is out-of-tolerance; will not close on "Go". (COMMON-TO: three of six, reported "Sterile" Examples)
The discrepancies pose problems for all of the theories, yet proposed. Both the unissued condition, and the survivability rate of a minor production group, mitigates toward rifles that were removed from their stands, at the point of Liberation, not subsequent to that event. Nor were they removed from any field.
We see the bayonet, from what may well be a five digit "F" series 'cut-away instruction aid', and one is tempted to think that such a rifle resided in proximity to the #486. When I first saw the handle I thought "prototype". But, no engineer would propose a debris-trap, for what is otherwise a sealed rifle.
I) The forearm of number 5 'Mystery Sterile', is patched, and was split when the bayonet copula was installed, (rejected part?). The bolt-face and extractor are as new.
II) A second view of the patch, which is not quite up to the usual quality of such repairs.